Electrochemical cells generally include an anode electrode and a cathode electrode separated by an electrolyte, where a proton exchange membrane (hereafter “PEM”) is used as the electrolyte. A metal catalyst and electrolyte mixture is generally used to form the anode and cathode electrodes. A well-known use of electrochemical cells is in a stack for a fuel cell (a cell that converts fuel and oxidants to electrical energy). In such a cell, a reactant or reducing fluid such as hydrogen or methanol is supplied to the anode, and an oxidant such as oxygen or air is supplied to the cathode. The reducing fluid electrochemically reacts at a surface of the anode to produce hydrogen ions and electrons. The electrons are conducted to an external load circuit and then returned to the cathode, while hydrogen ions transfer through the electrolyte to the cathode, where they react with the oxidant and electrons to produce water and release thermal energy.
Fuel cells are typically formed as stacks or assemblages of membrane electrode assemblies (MEAs), which each include a PEM, an anode electrode and cathode electrode, and other optional components. Fuel cell MEAs typically also comprise a porous electrically conductive sheet material that is in electrical contact with each of the electrodes and permits diffusion of the reactants to the electrodes, and is know as a gas diffusion layer, gas diffusion substrate or gas diffusion backing. When the electrocatalyst is coated on the PEM, the MEA is said to include a catalyst coated membrane (CCM). In other instances, where the electrocatalyst is coated on the gas diffusion layer, the MEA is said to include gas diffusion electrode(s) (GDE). The functional components of fuel cells are normally aligned in layers as follows: conductive plate/gas diffusion backing/anode electrode/membrane/cathode electrode/gas diffusion backing/conductive plate.
Long term stability of the PEM is critically important for fuels cells. For example, the lifetime goal for stationary fuel cell applications is 40,000 hours of operation. Typical membranes found in use throughout the art will degrade over time through decomposition and subsequent dissolution of the ion-exchange polymer in the membrane, thereby compromising membrane viability and performance. While not wishing to be bound by theory, it is believed that this degradation is a result, at least in part, of the reaction of the ion-exchange polymer of the membrane and/or the electrode with hydrogen peroxide (H2O2) radicals, which are generated during fuel cell operation. Fluoropolymer membranes are generally considered more stable in fuel cell operations than hydrocarbon membranes that do not contain fluorine, but even perfluorinated ion-exchange polymers degrade in use. The degradation of perfluorinated ion-exchange polymers is also believed to be a result of the reaction of the polymer with hydrogen peroxide.
Thus, it is desirable to develop a process for reducing or preventing degradation of a proton exchange membrane or membrane electrode assembly due to their interaction with hydrogen peroxide radicals, thereby sustaining performance while remaining stable and viable for longer periods of time, wherein as a result, fuel cell costs can be reduced.